A study of electrosorption selectivity of anions by activated carbon electrodes in capacitive deionization

Abstract The capacitive deionization (CDI) performance of activated carbon electrodes with various anions and competitive electrosorption between two anions in mixed solution were studied. It was found that the electrosorption capacity was strongly dependent on the ionic charge and hydrated radius. With the same concentration, smaller monovalent anions showed their size-affinity to access the pores. The order of normalized equivalent capacity was as follows: trivalent anion > divalent anion > monovalent anion. In mixed Cl − and NO 3 − solution, Cl − is preferably electrosorped over NO 3 − in early period of the electrosorption process. However, during the end of the electrosorption process, part of Cl − would be exchanged by NO 3 − due to the stronger competitiveness of NO 3 − than Cl − . There was no obvious selectivity between Cl − and SO 4 2 − .